Dutch police investigating how needles got into six turkey sandwiches on Delta Air Lines flights from Amsterdam to U.S. cities say the sandwiches and needles are being flown back to the Netherlands for tests.

Police at Amsterdam’s Schiphol Airport have opened a criminal investigation into how needles got into turkey sandwiches served to passengers on Delta Air Lines flights from Amsterdam to the United States, a spokesman said Tuesday. The FBI also is investigating the incidents.

Delta Air Lines reported a first-quarter profit on Wednesday as gains from hedging its fuel costs made up for losses in its day-to-day operations. The first three months of the year are usually the weakest for airlines because fewer people fly.